Atomic polar tensors , nuclear

Lazzeretti and coworkers175 calculated nuclear electric and electromagnetic shielding tensors for 1 and oxirane. These properties are related to atomic polar tensors and atomic axial tensors used by infrared and VCD spectroscopists. The authors demonstrated that they could obtain fairly accurate sum rules for atomic polar tensors and atomic axial tensors with relatively little computational effort. 

The second-rank molecular tensors, Pajg, are termed atomic polar tensors (APTs). Separating electronic and nuclear parts ... 

The derivative of the dipole moment with respect to the nuclear coordinates determines intensities of IR absorptions (Section 10.1.5). A central quantity in this respect is the Atomic Polar Tensor (APT), which for a given atom is defined in... 

Zitto et al formulated atomic populations different from those of AIM. They employed quantum-mechanical relationships involving the Atomic Polar Tensor and the related nuclear electric shielding, which provide clearcut recipes to evaluate atomic populations in molecules within the dipole acceleration formalism... 

Analysis of the derivatives of dipole moments with respect to nuclear displacements (the atomic polar tensors) gives rise to yet another definition of atomic charges. The GAPT (generalized atomic polar tensor) atomic charges ate... 

This theory was first formulated by Stephens (1985). In his approach to go beyond the Bom-Oppenheimer approximation, Stephens mixed excited electronic states with the ground state. Though that approach seemed to call for the difficult calculation of excited electronic states, he finally arrived at expressions, that only involve ground state properties. As an example to the application of the theory Jalkanen et al. (1989b) report nuclear shielding tensors, atomic polar and axial tensors, as well as IR and VCD intensities of the ammonia isotopomer N H (NHDT) using different basis sets. 

In the general case, polarizability is anisotropic it depends on the position of the molecnle with respect to the orientation of the external electric field. To consider the orientation, a is expressed by a fnnction — atom polarizability tensor — that defines the indnced dipole moment for each possible direction of the electric field. This atom polarizability tensor a describes the distortion in the nuclear arrangement in a molecnle (i.e., the tendency of polarization in three dimensions). The polarizability determined in an experiment is an average polarizability it is the sum of polarizabilities in three principal directions that are collinear with the external field [59],... 

K. J. Jalkanen, P. J. Stephens, P. Lazzeretti, and R. Zanasi, J. Chem. Phys., 90,3204 (1989). Nuclear Shielding Tensors, Atomic Polar and Axial Tensors, and Vibrational Dipole and Rotational Strengths of NHDT. 

Table 16-1. Energies, electric dipolar moments, net atomic populations, vibrational polarizabilities and mean vibrational molecular polarization, magnetizability and contributions thereto, isotropic g tensor and nuclear and electronic paramagnetic and diamagnetic contributions thereto, principal moments of inertia and rotational parameters calculated for H2 C N2 in seven structural isomers... 

---